摘要:

AbstractDye–macromolecule complexes provide good models for the study of the effects of coupling between chromophores. In addition to modifications of the visible and UV absorption spectra of the dyes at small interchromophore distances, very efficient energy transfer has been demonstrated at longer distances. The probability of nonradiative transition increases with the number of excitation transfers so that an array of oscillators close to one another becomes nonfluorescent. The insertion of a dye molecule, acting as a trap for the excitation energy, in the highly ordered system of chromophores constituted by the purine and pyrimidine bases of native DNA has given results supporting the intercalation model of Lerman and providing an experimental approach to the problem of the path length of energy migration in the DNA molecule. The average excitation path length seems to be of the order of only ten base pairs, a result which can explain the lack of fluorescence of the DN

ISSN:0006-3525    

DOI:10.1002/bip.360010502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

摘要:

AbstractThe Lifson‐Roig theory for the helix‐random coil transition in polyglycine has been modified to take side‐chain interactions into account. The modified theory is developed specifically for poly‐L‐alanine which probably contains a β1‐α4hydrophobic bond. A conditional probability, expressing the strength of such a hydrophobic bond, is evaluated from the Nemethy‐Scheraga data for the free energy of formation of the bond. This, together with the conditional probabilities for the states of the backbone chain, permit an evaluation of the partition function and properties of the helix‐random coil transition. It is seen that the hydrophobic bond renders the poly‐L‐alanine helix much more stable than the corresponding polyglycine one, in agreement with data obtaine

ISSN:0006-3525    

DOI:10.1002/bip.360010503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

摘要:

AbstractOptical, hydrodynamic, and titration properties of polyribouridylic acid (poly U) were investigated in 0.2MNa+, pH 6. Above 15°C., poly U was shown to be a randomly coiled single chain, devoid of secondary structure. There is no shear rate dependence of viscosity; molecular weight is independent of ionic strength; there is virtually no conformationally dependent hypochromicity; no anomalous optical rotatory dispersion; and no anomalous titration behavior. The dependence of the sedimentation constant and intrinsic viscosity on molecular weight was determined. Poly U was shown to be the most highly expanded of all synthetic and naturally occurring randomly coiled polynucleotides

ISSN:0006-3525    

DOI:10.1002/bip.360010504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

摘要:

AbstractThe effect of charges on sedimentation and diffusion of macroions is treated along the lines adopted by Svedberg‐Pedersen for the description of sedimentation, with the difference that the virtual electrophoretic motion of the macroions which gives rise to the charge effect is not equated to the real electrophoretic mobility. Furthermore the activity correction is introduced through the recently established representation, according to which a constant fraction of the counter‐ions may be considered to be permanently immobilized. Lastly, for the sake of simplicity, it is assumed that the frictional coefficient of the macroions does not depend on the ionic strength. On this basis a relatively simple description in terms of readily accessible parameters is obtained. The charge effects in sedimentation and diffusion are closely related, one to another, and to other polyelectrolyte properties. The physical significance of the results is discussed. The description is compared to experimental data in the literature and also to the second experimental part of this work: it is found that the main features of the charge effect are satisfactorily described under widely differing conditions, although some deviations indicate the limitations of the approximate treatm

ISSN:0006-3525    

DOI:10.1002/bip.360010505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

摘要:

AbstractThe sedimentation, diffusion, and osmotic behavior of poly‐L‐lysine hydrochloride is examined over a wide range of ionic strengths and in solutions which range in relative composition from a swamping excess of added salt (suppression of charge effect) to salt‐free solutions (maximum effect). The charge effect is found to essentially obey the theoretical treatment proposed in Part I of this work. The frictional coefficient of the macroion in salt‐free solutions is comparable to that of the fully stretched chain. In excess of salt the friction is appreciably smaller, its magnitude not varying greatly with ionic strength. The molecular weight is determined osmotically and also from diffusion‐sedimentation, with the charge effect suppressed by addition of salt or eliminated through the use of non‐ionized forms of the polymer; a reasonable agreement is obtained between the methods. The influence of small ions on sedimentation is also examined. The secondary salt effect is found to be much smaller than that predicted theoretically; on the other hand, the substitution of different counterions in the absence of secondary salt effect gives rise to changes of the expecte

ISSN:0006-3525    

DOI:10.1002/bip.360010506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360010507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360010508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360010501

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1963

数据来源: WILEY